Activation of the p21(CIP1/WAF1) promoter by bone morphogenetic protein-2 in mouse B lineage cells

Zoledronate induces cell cycle arrest and differentiation by upregulating p21 in mouse MC3T3-E1 preosteoblasts

Background: Increasing research has recently been focused on the supplementary use of drugs such as bisphosphonates that are known to influence bone turnover to prevent and treat periprosthetic bone loss and subsequent implant loosening following total joint replacements. However, there are still concerns about the conflicting effects of bisphosphonate treatment on osteoblastic bone formation in the literature. Methods: In this study, we investigate the role of zoledronate (ZOL) in regulating cell cycle distribution and differentiation in mouse MC3T3-E1 preosteoblasts and also explore the mechanism underlying this effect of ZOL. We examined the expression levels of osteocalcin (OCN) by quantitative polymerase chain reaction (qPCR), the total amount of CDK6, p21 and p27 proteins by Western blot analysis, and the cell cycle distribution by flow cytometric analysis in mouse MC3T3-E1 preosteoblasts to evaluate the effect of ZOL. Small interfering RNAs (siRNAs) were used to assess the individual contributions of genes to specific osteoblast phenotypes. Results: In addition to increased OCN expression, we found that ZOL treatment induces the G₀/G₁ arrest and results in the increase of p21 and p27 expressions and decrease of CDK6 expression in mouse MC3T3-E1 preosteoblasts. Both p21 and p27 mediates ZOL-induced cell cycle exit; however, p21, but not p27, is responsible for the increase of ZOL-induced OCN expression in these cells. Conclusions: These results endorse that ZOL might have an anabolic effect on osteoblasts. The CDK inhibitor p21 plays a key role in regulating osteoblast differentiation by controlling proliferation-related events in mouse MC3T3-E1 preosteoblasts.

Epigenetic approaches for chemosensitization of refractory diffuse large B-cell lymphomas

Diffuse large B-cell lymphoma (DLBCL) is the most common form of non-Hodgkin lymphoma, with the greatest challenge for improving patient survival being the management of chemorefractory disease upon relapse. Epigenetic dysregulation has been correlated with more-aggressive malignancies and chemoresistance. In this issue of Cancer Discovery, Clozel and colleagues show the potential for low-dose DNA methyltransferase inhibitors as both a rational and an effective neoadjuvant approach for chemosensitization in DLBCL.

BMP signaling induces astrocytic differentiation of clinically derived oligodendroglioma propagating cells

Oligodendrogliomas are a type of glioma that lack detailed investigation because of an inability to cultivate oligodendroglioma cells that faithfully recapitulate their salient qualities. We have successfully isolated and propagated glioma stem-like cells from multiple clinical oligodendroglioma specimens. These oligodendroglioma-propagating cells (OligPC) are multipotent and form xenografts with oligodendroglioma features. Bone morphogenetic proteins (BMP) are considered potent inhibitors of oligodendrogliogenesis during development; therefore, the effects of BMP signaling in OligPCs were characterized. BMP pathway components are expressed by OligPCs and canonical signaling via Smad proteins is intact. This signaling potently depletes CD133-positive OligPCs, decreasing proliferation, and inducing astrocytic differentiation. Furthermore, analyses revealed that cytoplasmic sequestration of the oligodendrocyte differentiation factors OLIG1/2 by the BMP signaling effectors ID2 and ID4 is a plausible underlying mechanism. These findings elucidate the molecular pathways that underlie the effects of BMP signaling on oligodendroglioma stem-like cells.

IMPLICATIONS

Stem-like cells are capable of propagating oligodendrogliomas, and BMP signaling potently diminishes their stemness by inducing astrocytic differentiation, suggesting that BMP activation may be effective as a cancer stem cell-targeted therapy.

Mechanism-based epigenetic chemosensitization therapy of diffuse large B-cell lymphoma

Although aberrant DNA methylation patterning is a hallmark of cancer, the relevance of targeting DNA methyltransferases (DNMT) remains unclear for most tumors. In diffuse large B-cell lymphoma (DLBCL) we observed that chemoresistance is associated with aberrant DNA methylation programming. Prolonged exposure to low-dose DNMT inhibitors (DNMTI) reprogrammed chemoresistant cells to become doxorubicin sensitive without major toxicity in vivo. Nine genes were recurrently hypermethylated in chemoresistant DLBCL. Of these, SMAD1 was a critical contributor, and reactivation was required for chemosensitization. A phase I clinical study was conducted evaluating azacitidine priming followed by standard chemoimmunotherapy in high-risk patients newly diagnosed with DLBCL. The combination was well tolerated and yielded a high rate of complete remission. Pre- and post-azacitidine treatment biopsies confirmed SMAD1 demethylation and chemosensitization, delineating a personalized strategy for the clinical use of DNMTIs.

SIGNIFICANCE

The problem of chemoresistant DLBCL remains the most urgent challenge in the clinical management of patients with this disease. We describe a mechanism-based approach toward the rational translation of DNMTIs for the treatment of high-risk DLBCL.

Major signaling pathways in intestinal stem cells

BACKGROUND

The discovery of markers to identify the intestinal stem cell population and the generation of powerful transgenic mouse models to study stem cell physiology have led to seminal discoveries in stem cell biology.

SCOPE OF REVIEW

In this review we give an overview of the current knowledge in the field of intestinal stem cells (ISCs) highlighting the most recent progress on markers defining the ISC population and pathways governing intestinal stem cell maintenance and differentiation. Furthermore we review their interaction with other stem cell related pathways. Finally we give an overview of alteration of these pathways in human inflammatory gastrointestinal diseases.

MAJOR CONCLUSIONS

We highlight the complex network of interactions occurring among different pathways and put in perspective the many layers of regulation that occur in maintaining the intestinal homeostasis.

GENERAL SIGNIFICANCE

Understanding the involvement of ISCs in inflammatory diseases can potentially lead to new therapeutic approaches to treat inflammatory GI pathologies such as IBD and celiac disease and could reveal the molecular mechanisms leading to the pathogenesis of dysplasia and cancer in inflammatory chronic conditions. This article is part of a Special Issue entitled Biochemistry of Stem Cells.

WNT signaling increases proliferation and impairs differentiation of stem cells in the developing cerebellum

The WNT pathway plays multiple roles in neural development and is crucial for establishment of the embryonic cerebellum. In addition, WNT pathway mutations are associated with medulloblastoma, the most common malignant brain tumor in children. However, the cell types within the cerebellum that are responsive to WNT signaling remain unknown. Here we investigate the effects of canonical WNT signaling on two important classes of progenitors in the developing cerebellum: multipotent neural stem cells (NSCs) and granule neuron precursors (GNPs). We show that WNT pathway activation in vitro promotes proliferation of NSCs but not GNPs. Moreover, mice that express activated β-catenin in the cerebellar ventricular zone exhibit increased proliferation of NSCs in that region, whereas expression of the same protein in GNPs impairs proliferation. Although β-catenin-expressing NSCs proliferate they do not undergo prolonged expansion or neoplastic growth; rather, WNT signaling markedly interferes with their capacity for self-renewal and differentiation. At a molecular level, mutant NSCs exhibit increased expression of c-Myc, which might account for their transient proliferation, but also express high levels of bone morphogenetic proteins and the cyclin-dependent kinase inhibitor p21, which might contribute to their altered self-renewal and differentiation. These studies suggest that the WNT pathway is a potent regulator of cerebellar stem cell growth and differentiation.

Differential gene expression in non-malignant tumour microenvironment is associated with outcome in follicular lymphoma patients treated with rituximab and CHOP

Rituximab in combination with chemotherapy (immunochemotherapy) is one of the most effective treatments available for follicular lymphoma (FL). This study aimed to determine whether differences in gene expression in FL tissue correlate with outcome in response to rituximab and CHOP (cyclophosphamide, doxorubicin, vincristine, prednisone) chemotherapy (R-CHOP). We divided 24 patients into long- [time to treatment failure (TTF) >35 months] and short-term (TTF <23 months) responders, and analysed the gene expression profiles of lymphoma tissue using oligonucleotide microarrays. We used a supervised learning technique to identify genes correlating with outcome, and confirmed the expression of selected genes with quantitative polymerase chain reaction (qPCR) and immunohistochemistry. Among the transcripts with a high correlation between microarray and qPCR analyses, we identified EPHA1, a tyrosine kinase involved in transepithelial migration, SMAD1, a transcription factor and a mediator of bone morphogenetic protein and transforming growth factor-beta signalling, and MARCO, a scavenger receptor on macrophages. According to Kaplan-Meier estimates, high EPHA1, and low SMAD1 and MARCO expression were associated with better progression-free survival (PFS). Immunohistochemistry showed that EphA1 was primarily localised in granulocytes. In addition, both EphA1 and Smad1 were expressed in vascular endothelia. However, no difference in vasculature was detected between long- and short-term responders. In a validation set of 40 patients, a trend towards a better PFS was observed among patients with high EphA1 expression. We conclude that gene expression in non-malignant cells contributes to clinical outcome in R-CHOP-treated FL patients.

Execution of BMP-4-induced apoptosis by p53-dependent ER dysfunction in myeloma and B-cell hybridoma cells

Bone morphogenic protein (BMP)-4 inhibits proliferation and induces the apoptosis of myeloma cells. However, little is known about the molecular mechanisms of how BMP-4 executes this apoptosis. In this report, we investigated the roles of p53 and the endoplasmic reticulum (ER) in BMP-4-induced apoptosis of mouse hybridoma HS-72 cells. We found that 3 ng/ml of BMP-4 is sufficient to induce the expression of proapoptotic proteins, puma and bax, in a p53-dependent mechanism, and facilitate Ca(2+) release from the ER to the cytosol, resulting in the activation of caspase-12 and ER dysfunction. Similarly to HS-72 cells, multiple myeloma cells with wild-type p53 genes show much higher sensitivity to BMP-4-induced apoptosis than cells without wild-type p53 genes, suggesting that wild-type p53 status is required for dysfunction of the ER during BMP-4-induced apoptosis in ER-enriched cells, such as hybridoma and myeloma cells. These findings demonstrate that the presence of wild-type p53 genes and enrichment of the ER determines the sensitivity to effective apoptosis by BMP-4, and suggest that ER stress-inducing agents would be valuable in the treatment of multiple myeloma.

Smad pathway-specific transcriptional regulation of the cell cycle inhibitor p21WAF1/Cip1

Transforming growth factor-beta (TGF-beta) inhibits epithelial cell growth, in part via transcriptional induction of the cell cycle inhibitor p21(WAF1/Cip1) (p21). We show that bone morphogenetic protein (BMP)-7 induces higher p21 expression than TGF-beta1 in various epithelial cells. Despite this, BMP-7 only weakly suppresses epithelial cell proliferation, as Id2, a cell cycle-promoting factor, becomes concomitantly induced by BMP-7. Signaling studies with all type I receptors of the TGF-beta superfamily show that BMP receptors induce higher p21 expression than TGF-beta/activin receptors. Smad4 is essential for p21 regulation by all receptor pathways. Based on the previously known ability of c-Myc to block p21 expression and epithelial growth arrest in response to TGF-beta1, we demonstrate that ectopic c-Myc expression can abrogate Smad-mediated p21 induction by all TGF-beta and BMP receptors. Furthermore, p21 induction by all receptor pathways can be blocked by the natural inhibitors of the TGF-beta superfamily. Smad7 inhibits all pathways whereas Smad6 selectively inhibits the BMP pathways. The observed pathway specificity reflects the efficiency by which BMP Smads, compared to TGF-beta Smads, transactivate the p21 promoter. In addition, BMP-specific Smads, Smad1, Smad5, and especially Smad8, induce endogenous p21 mRNA and protein levels, while they fail to induce epithelial growth inhibition when compared to TGF-beta receptor-phosphorylated Smads (R-Smads), Smad2 and Smad3. Thus, p21 is a common target of all TGF-beta superfamily pathways. However, the ability of TGF-beta superfamily members to induce cell growth arrest depends on the regulation of additional gene targets.

BMP signaling initiates a neural crest differentiation program in embryonic rat CNS stem cells

Bone morphogenetic proteins (BMPs) have an important role in neuronal and astrocytic differentiation of embryonic and adult neural stem cells (NSCs). Here, we show that BMP6, BMP7, GDF5, and GDF6 instructively differentiate E12, E14, and E17 rat cortical NSCs into a variety of neural crest lineages. Clonal analysis shows that BMP7-treated NSCs develop mostly into smooth muscle and peripheral glia. We observed a rapid induction of premigratory neural crest markers like p75NTR, and AP-2 alpha followed by Msx1, Msx2, and Slug, transcription factors that participate in neural crest development. These results suggest that NSCs cultured in vitro in the presence of FGF2 display expanded developmental potential.

Interplay between the tumor suppressor p53 and TGF beta signaling shapes embryonic body axes in Xenopus

The transcription factor p53 has been shown to mediate cellular responses to diverse stresses such as DNA damage. However, the function of p53 in cellular differentiation in response to growth factor stimulations has remained obscure. We present evidence that p53 regulates cellular differentiation by modulating signaling of the TGF beta family of growth factors during early Xenopus embryogenesis. We show that p53 functionally and physically interacts with the activin and bone morphogenetic protein pathways to directly induce the expression of the homeobox genes Xhox3 and Mix.1/2. Furthermore, functional knockdown of p53 in embryos by an antisense morpholino oligonucleotide reveals that p53 is required for the development of dorsal and ventral mesoderm. Our data illustrate a pivotal role of interplay between the p53 and TGF beta pathways in cell fate determination during early vertebrate embryogenesis.

Bone morphogenetic protein-2 restores mineralization in glucocorticoid-inhibited MC3T3-E1 osteoblast cultures

The anti-glucocorticoid potential of BMP-2 in osteoblasts was tested in MC3T3-E1 cells using dexamethasone (1 microM) and rhBMP-2 (10 or 100 ng/ml). rhBMP-2 restored mineralization but not condensation or collagen accumulation. These results demonstrate the potential and limitations of BMPs in counteracting glucocorticoids.

INTRODUCTION

Pharmacologic glucocorticoids (GCs) inhibit osteoblast function and induce osteoporosis. Bone morphogenetic proteins (BMPs) stimulate osteoblast differentiation and bone formation. Here we tested the anti-glucocorticoid potential of BMP-2 in cultured osteoblasts.

MATERIALS AND METHODS

MC3T3-E1 cells were treated with dexamethasone (DEX; 1 microM) and/or recombinant human BMP-2 (rhBMP-2; 10 or 100 ng/ml). Culture progression was characterized by cell cycle profiling, biochemical assays for DNA, alkaline phosphatase (ALP), collagen, and calcium, and by reverse transcriptase-polymerase chain reaction (RT-PCR) of osteoblast phenotypic mRNAs. Mineralization was characterized by Alizarin red and von Kossa staining and by Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD).

RESULTS

DEX inhibited differentiation-related cell cycle, nodule formation, collagen accumulation, osteocalcin, and BMP-2 gene expression as well as mineralization. Replenishment of GC-inhibited cultures with 10 or 100 ng/ml rhBMP-2 dramatically rescued mineral deposition. The rhBMP-2-rescued mineral was bone-like apatite nearly identical to the mineral of control cultures. The rhBMP-2 rescue was associated with increased mRNA levels for alpha1(I) collagen, osteocalcin, and Cbfa1 types I and II, as well as ALP activity. In contrast, rhBMP-2 did not rescue the GC-inhibited differentiation-related cell cycle, nodule formation, or collagen accumulation. When administered alone, rhBMP-2 also increased the mRNA levels for alpha1(I) collagen, osteocalcin, and Cbfa1 types I and II, as well as ALP activity. However, treatment with rhBMP-2 alone inhibited cell cycle progression, nodule formation, and collagen accumulation. Surprisingly, in contrast to its rescue of mineralization in DEX-treated cultures, rhBMP-2 inhibited mineralization in the absence of DEX. In parallel to its bimodal effect on mineralization, rhBMP-2 stimulated endogenous BMP-2 mRNA in the presence of DEX, but inhibited endogenous BMP-2 mRNA in the absence of DEX.

CONCLUSIONS

Suppression of BMP-2 gene expression plays a pivotal role in GC inhibition of osteoblast differentiation. However, the inability of rhBMP-2 to rescue the entire osteoblast phenotype suggests BMP-2-independent inhibitory effects of CCs. BMP-2 exerts both positive and negative effects on osteoblasts, possibly depending on the differentiation stage and/or the existing BMP signaling.

Bone morphogenetic proteins and their antagonists in skin and hair follicle biology

Bone morphogenetic proteins (BMP) are members of the transforming growth factor-beta superfamily regulating a large variety of biologic responses in many different cells and tissues during embryonic development and postnatal life. BMP exert their biologic effects via binding to two types of serine/threonine kinase BMP receptors, activation of which leads to phosphorylation and translocation into the nucleus of intracellular signaling molecules, including Smad1, Smad5, and Smad8 ("canonical" BMP signaling pathway). BMP effects are also mediated by activation of the mitogen-activated protein (MAP) kinase pathway ("noncanonical" BMP Signaling pathway). BMP activity is regulated by diffusible BMP antagonists that prevent BMP interactions with BMP receptors thus modulating BMP effects in tissues. During skin development, BMPs its receptors and antagonists show stringent spatiotemporal expressions patterns to achieve proper regulation of cell proliferation and differentiation in the epidermis and in the hair follicle. In normal postnatal skin, BMP are involved in the control of epidermal homeostasis, hair follicle growth, and melanogenesis. Furthermore, BMP are implicated in a variety of pathobiologic processes in skin, including wound healing, psoriasis, and carcinogenesis. Therefore, BMPs represent new important players in the molecular network regulating homeostasis in normal and diseased skin. Pharmacologic modulation of BMP signaling may be used as a new approach for managing skin and hair disorders.

A novel therapeutic approach for hematological malignancies based on cellular differentiation and apoptosis

Hematological malignancies including acute leukemia, and multiple myeloma are disorders characterized by the accumulation of neoplastic hematopoietic cells, resulting in aggressive clinical manifestations with poor prognosis. The therapeutic approach to these disorders is basically chemotherapy for achieving complete remission based on the concept of total cell kill. However, severe side effects and complications such as serious infection and bleeding due to anti-cancer drugs are major problems in the clinical setting. In addition, repeated episodes of relapse of the disease may lead to refractory or chemotherapy-resistant disorders. These problems are occurred because anti-cancer agents have effects on both cancer cells and normal hematopoietic cells. The clinical evidences thus suggest the limitations of the chemotherapy for hematological malignancies: novel effective therapeutic approaches with less toxicity are therefore actively being sought. Differentiation-inducing therapy employing a physiologically active derivative of vitamin A, all-trans retinoic acid (ATRA), brought remarkably advances in the therapeutic outcome of APL at the end of last century. More recently, the clinical success of imatinib mesylate (STI571), potent competitive inhibitor of the Bcr/Abl protein tyrosine kinase, in the treatment of CML has focused enthusiasm toward molecular targeted therapy for the hematological malignancies. The therapeutic activity of these agents can be explained by their abilities to modify cellular growth, differentiation, and apoptosis in cells by activating unknown gene programs that molecular cellular proliferation. We have actively sought out new agents among natural products and cytokines with the ability to induce cellular differentiation and apoptosis. In this symposium, I will present our recent data of these novel compounds and their molecular mechanisms for inducing differentiation and apoptosis of hematological malignant cells.

Bone morphogenetic protein (BMP)-2 induces apoptosis in human myeloma cells

BMPs (bone morphogenetic proteins), members of the transforming growth factor (TGF)-beta superfamily, are a group of related proteins which are capable of inducing the formation of cartilage and bone, but are now regarded as multifunctional cytokines. However, little is known about their role in hematopoiesis. Recently, we found a novel function of BMPs to hematopoietic cells in that BMP-2 induces apoptosis not only in human myeloma cell lines, but also in primary samples from patients with multiple myeloma in vitro. BMP-2 caused cell cycle arrest in the G1 phase which was associated with accumulation of p21CIP1/WAF1 and p27KIP1, and the subsequent apoptosis of myeloma cells. Further analysis showed that BMP-2 induced down-regulation of Bcl-X(L) through the inactivation of STAT3, resulting in the induction of apoptosis in myeloma cells. We conclude that BMP-2 may have the potential to be one of the novel therapeutic agents for treatment in patients with multiple myeloma because of the beneficial effects on both myeloma cells and bone diseases. In this review, we summarize data concerning BMPs and BMP-2-induced apoptosis of myeloma cells including our own recent experimental data.